The present invention relates to a communication apparatus, and more particularly to a speech signal communication apparatus for use in a confidential communication system.
Requirements for a confidential communication system are high sound quality and high confidentiality under the limitation of transmission capacity of a given transmission line, such as a public communication telephone line, and these requirements are in a trade-off relationship.
The deformation processing and restoration processing of a speech signal for a confidential communication system are performed by linear arithmetic processes and, where high confidentiality and accordingly complex processing are required, entails blockwise processing, such as FFT.
A prior art confidential communication system entailing complex blockwise processing, when it deforms, transmits and restores a speech signal having a waveform shown in FIG. 1(a) for instance, is limited in the reproducibility of the waveform because of the constraint of the arithmetic capacity and the nonlinearity of the transmission line among other things, and accordingly has the disadvantage that discontinuity of the waveform arises on the block boundary in the restored speed signal, as shown in FIG. 1(b), resulting in poor sound quality.